How does Solar Impulse work?

All images courtesy of Solar Impulse

First in Flight

Today, the Solar Impulse plane becomes the first aircraft powered only by the Sun to make an international journey. Taking off from Payerne in Switzerland, the plane touched down at Brussels Airport to complete a 12 hour journey.

While it has completed several journeys before, including between Geneva and Zurich airports, the international trip to Belgium through crowded European airspace is regarded as much more of a challenge. The aircraft is piloted by co-founder Andre Borschberg, the other being Bertrand Piccard.

“Flying an aircraft like Solar Impulse through European airspace to land at an international airport is an incredible challenge for all of us, and success depends on the support we receive from all the authorities concerned,” said Borschberg.

Pioneering green technologies, the aircraft is on display at Brussels airport until May 29 and will then fly to Paris for the international air show at Le Bourget from June 20 to 26.

The Solar Impulse holds the record for the longest continuous flight using solar power at 26 hours, 19 minutes and 10 seconds. It is hoped that, when a larger plane version of the Solar Impulse is completed in 2013 or 2014, it will be able to complete a journey around the world.

How It Works

Harnessing the power of the Sun, the Solar Impulse project aims to fulfil a very grand ambition, to produce the first aircraft capable of perpetual flight. It would be the first aircraft to fly round the world without ever needing to refuel, propelled through solar power.

The Solar Impulse works by sporting a wingspan the size of an Airbus A340 (63.40 metres) layered with state-of-the-art solar monocrystalline silicon cells, each 150 microns thick and chosen for their lightness, flexibility and efficiency. This massive wingspan is partnered by a super lightweight fuselage (1,600kg) built round a carbon fibre-honeycomb composite using a sandwich structure of a series of 120 carbon fibre ribs. Attached to the wings are four gondolas each containing a 10hp motor, a lithium polymer battery set and a management system controlling charge/discharge and temperature. Surrounding these is a raft of thermal insulation used to conserve the heat radiated from the batteries and keep them functioning at 8,500 metres, where the temperature can drop to -40°C. Its cockpit, where every piece of instrumentation has been specially developed and redesigned to save energy, is also cutting-edge.

In order to conserve energy – critical to the night flight portion of this planned 36-hour world tour – each of the Solar Impulse’s twin-bladed propellers, which are capable of operating in a 200-4,000rpm range, are limited by a reducer to ensure energy is not wasted when solar energy is in abundance. Indeed, the statistics point to this being one of the most important challenges faced by the Solar Impulse. At midday each metre-square piece of Earth receives the equivalent of 1,000 watts of solar power, a figure that over a 24 hour period averages out at just 250W/m2, or in other terms, enough power for each of the engines to produce only 8hp. This means as little energy as possible needs to be wasted during the more prolific day, as it needs to be stored for the night time where the battery reserves are all that stands in the way of the Impulse losing total power.

Amazingly, the 8hp produced by the Solar Impulse’s engines is the same amount of power the Wright brothers had available to them in their historic 1903 flight.